Various powders exemplified by white and colored pigments such as titanium oxide, zinc oxide, red iron oxide, and the like and extender pigments such as mica, sericite, and the like are widely used in the fields of basic cosmetic compositions and other various cosmetic compositions such as sunscreens, nail colors, nail coats, foundations, mascaras, eye liners, and the like. However, untreated powder is prone to agglomerate due to the electric charge and polarity, trace amount of impurities, and the like on the powder surface. Therefore, powders that have been subject to various surface treatments are widely used for the purpose of enhancing dispersibility and stability of a powder in a cosmetic composition and also improving the tactile sensation, moisture resistance, sebum resistance, and the like of a cosmetic composition comprising a powder.
Known examples of such surface treatments include lipophilization treatments using an oil agent, a metal soap, or the like; hydrophilization treatments using a surfactant, water-soluble polymer, or the like; hydrophobization treatments using silicone compounds; silica treatments; alumina treatments; and the like. Particularly, in recent years, there have been many cases where a surface treatment using a silicone compound having a reactive moiety in the molecule have been performed. The reactive moiety forms a chemical bond with the powder surface and, as a result, the surface treatment using the silicone compound is effective from the perspective of simultaneously modifying the surface of the powder and blocking the surface activity of the powder. Additionally, because surface treatment can be thoroughly performed, the surface treatment agent will not separate from the powder surface, even when compounded in a cosmetic composition comprising a solvent. Moreover, changes in properties of the powder due to the surface treatment can be kept to a minimum. An example of such a surface treatment is a method in which a powder is surface treated using a methylhydrogenpolysiloxane (Patent Document 1). However, in this method, unreacted Si—H groups still remain even after the surface treating of the powder and, therefore, there is a problem when this powder is compounded in a cosmetic composition because hydrogen gas may be produced depending on the components and the like in the cosmetic composition.
On the other hand, methods for manufacturing a powder dispersion using a hydrophilic group-modified organopolysiloxane that has good compatibility with the powder surface. Examples thereof include a method for forming a polyether-modified organopolysiloxane into a powder dispersing aid (Patent Document 2) and a method for forming an organopolysiloxane modified by polyglycerine or a similar polyhydric alcohol into a powder dispersing aid (Patent Document 3). However, there are problems in that the powder dispersion effectiveness is still insufficient, viscosity of a power dispersion obtained by dispersing a powder in silicone oil or a similar oil agent increases gradually over time, fluidity is lost, and the like.
As a method to resolve the problems described above, the present applicant has proposed methods using a co-modified organopolysiloxane copolymer having a group that has a carbosiloxy dendron structure and a glycerin derivative, polyhydric alcohol, or similar hydrophilic group in the molecule (Patent Documents 4, 5, and 6). Such co-modified organopolysiloxanes are safe and do not produce hydrogen, and can be advantageously used in the surface treating of a powder. Moreover, affinity with other raw materials of cosmetic compositions is superior, and the dispersibility and stability of the powder in a cosmetic composition comprising a powder can be enhanced.
However, the co-modified organopolysiloxane copolymers described in Patent Documents 4 to 6 have a large content of hydrophilic groups and many hydroxyl groups, and the viscosity of the copolymer itself tend to increase due to cohesive force resulting from hydrogen bonding. Thus, performance is insufficient from the perspective of handling/workability in cases when used as a powder treatment agent. Additionally, efficiency tends to decline when fabricating a dispersion and, thus, the performance of these co-modified organopolysiloxane copolymers is insufficient from the perspective of the dispersibility of powder.